| Abstract: | The effect of urea leaf treatment on plant growth and rhizosphere microorganisms was studied under controlled environmental conditions with spring wheat at 2 growth stages, and at 2 inorganic nutrient levels of the soil. The increase in dry weight of shoots and roots was inhibited by the urea treatment. Treatment of seedlings also resulted in a delay in the formation of tillers and nodal roots, especially in low fertilized soil. A temporary increase of rhizoplane bacteria was demonstrated after 7–9 days due to a stimulation of fast growing strains. A quantitative effect on rhizoplane fungi was only apparent, on day 9 after treatment of seedlings, as a decrease in total numbers and coincided with the increase in numbers of bacteria and actinomycetes. At this time the numbers of fungi known to be early root colonizers like Penicillium spp. and Mortierella spp. decreased after initially being stimulated, while numbers of late colonizers like Fusarium spp. and Trichoderma spp. increased after 9 days after initially being reduced in comparison with the control. Investigation of the rhizosphere effect (R/S) of wheat by the soil dilution plate method and fluorescence microscopy showed a 200% increase in total numbers of micro-organisms in the rhizosphere soil when the former method was used, but a 10–30% reduction when fluorescence microscopy was employed. |
